To make a straw thermometer, you need an 11-ounce, clear, plastic water bottle; clear, plastic drinking straw; modeling clay; food coloring; two plastic containers; ice; and a thermometer. Fill the bottle with room temperature water and add food coloring until you get the desired color. Roll modeling clay into a 5-inch or 6-inch long “snake.” Submerge one end of the straw 3 inches beneath the water in the bottle. Wrap the clay snake snugly around the circumference of the straw at the level of the bottle's opening and use it to seal the opening of the bottle. Carefully push down on the clay without breaking the seal to make the colored water rise up the straw 2 inches higher than the clay. When you push down on the clay, there is less room in the bottle and some of the liquid goes up the straw.
Fill one of the containers with cold water and add ice. Fill the other container with very hot water. Put the "straw thermometer" -- the water bottle with the straw held in the opening by clay -- in the ice water container. The colored water in the straw drops because the ice water cools the water in the thermometer. As water molecules cool, they move more slowly and take up less space -- volume. Allow the thermometer to warm up to room temperature. Put it into the container of hot water. The level of water in the straw rises because heat speeds up the molecules and the water volume expands. With nowhere else for the water to go, it rises up the straw.
You can calibrate your straw thermometer to read the temperature instead of just indicating whether the temperature is rising or falling. With the water in the thermometer at room temperature, measure the room temperature with the already calibrated thermometer. Mark the water level and note the temperature. Continue to take temperature readings throughout the day and in locations where it is warmer or colder. Follow the weather report and check the accuracy of your straw thermometer.
Try other liquids in your straw thermometer to see which ones have a larger change in volume when heated or cooled. Some liquids to try include an equal mixture of water and rubbing alcohol, undiluted rubbing alcohol, or a non-carbonated, sugar-sweetened soft drink. Re-calibrate your thermometer for each of the other liquids and compare the height of the liquid in the straw at various temperatures.